The present invention relates generally to hydraulic dampers or shock absorbers adapted for use in a suspension system such as the suspension systems used for automotive vehicles. More particularly, the present invention relates to a single piece piston having a sealing land design and a fluid passage design which allow manufacture of the single piece piston by powdered metal processes.
Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to the unsprung portion of tile vehicle. The piston is connected to the sprung portion of the automobile through a piston rod which extends through the pressure tube. The piston divides the pressure tube into an upper working chamber and a lower working chamber both of which are filled with hydraulic fluid. Because the piston is able, through valving, to limit the flow of the hydraulic fluid between the upper and the lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle of the vehicle. In a dual tube shock absorber, a fluid reservoir or reserve chamber is defined between the pressure tube and a reserve tube. A base valve is located between the lower working chamber and the reserve chamber to also produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung portion of the vehicle to the sprung portion of the automobile.
As stated above, the valving on the piston limits the flow of damping fluid between the upper and lower working chambers when the shock absorber is compressed or extended. During driving, the suspension system moves in jounce (compression) and rebound (extension). During jounce movements, the shock absorber is compressed causing damping fluid to move through the piston from the lower working chamber to the upper working chamber. A one-way check valve is normally located on the upper side of the piston to control the flow of damping fluid and thus the damping force created. During rebound movements, the shock absorber is extended causing damping fluid to move through the piston from the upper working chamber to the lower working chamber. A one-way check valve is normally located on the lower side of the piston to control the flow of damping fluid and thus the damping force created.
The piston normally includes a plurality of compression passages and a plurality of extension passages extending through the body of the piston. The compression check valve on the upper side of the piston opens the compression passages during jounce or compression movements of the shock absorber and closes the compression passages during rebound or extension movements of the shock absorber. Similarly, the extension check valve on the lower side of the piston opens the extension passages during rebound or extension movements of the shock absorber and closes the extension passages during jounce or compression movements of the shock absorber. Thus, the compression check valve must not interfere with the inlet to the extension passages and the extension check valve must not interfere with the inlet to the compression passages.
In order to avoid interference between the check valves and their opposing fluid passages, various non-interference methods have been designed into the piston. One method is to incorporate a radial offset between the compression passages and the extension passages. In this manner, one inlet is located radially outward of its opposing check valve and the opposite inlet is located radially inward of its opposing check valve. Another method is to angle the compression passages in one direction while angling the extension passages in the opposite direction. In this manner, both sets of inlets are located radially inward and both sets of outlets are located radially outward.
While the various methods for avoiding interference between the check valves and their opposing fluid passages have met with commercial success, continued development of shock absorber pistons includes development of lower cost systems enabling lower cost manufacturing for the piston itself, the valving system and thus the cost for the shock absorber.
The present invention provides the art with a single piece piston design which has an upper side which is identical to its lower side but rotated 45xc2x0 from each other. The sealing lands on each side of the piston have a unique shape which eliminates interference between the check valves and their opposing passages. In one embodiment, the passages are formed in an S shape and in a second embodiment, the passages are formed straight. Both embodiments enable the single piece piston to be manufactured by powered metal processes.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.